Biochemical methane potential of three-phase olive mill solid waste: Influence of temperature and supplemental enzymes

Abstract

Methane potential of three-phase olive mill solid waste (3POMSW) was evaluated by biochemical methane potential (BMP) tests at temperatures of 37.5 °C and 55 °C. The results have shown, that thermophilic processing has a higher methane and biogas yield by 10% and 17.2%, respectively, compared to mesophilic conditions. Concluding thermophilic conditions of 3POMSW results in higher conversion of the feedstock into biogas. The result of addition of enzymes (MethaPlus, Hemicellulase, PectinaseL, Amylase S and Lipase) and their mixtures to 3POMSW at 55 °C has shown that the optimum mixture of enzymes was Metha Plus and Hemicellulase, which resulted in an increase of methane yield by 1.3% compared to the base case without addition of enzymes. Simple model equations were developed based on first-order kinetic in order to calculate the biogas yield versus the time as a function of reaction rate constant (k) and the maximum biogas yield (ymax). In this study, results have shown two different reaction rates obtained for the mixtures of enzymes with 3POMSW of 0.130 d−1 from t = 0…14 days and 0.034 d−1 from t = 28…63 days. The developed simple model equations can be applied for calculating the biogas yield at the time and by optimizing the process improving biological nutrient removal.